Supercritical water process to upgrade petroleum

ABSTRACT

Provided is a process for the supercritical upgrading of petroleum feedstock, wherein the process includes the use of a start-up agent, wherein the use of the start-up agent facilitates mixing of the petroleum feedstock and water, thereby reducing or eliminating the production of coke, coke precursor, and sludge.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/553,758, filed on Oct. 31, 2011, the disclosure of which isincorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to process for the upgrading of petroleum. Morespecifically, the invention relates to a process for the supercriticalupgrading of petroleum to provide a desulfurized, upgraded hydrocarbonstream.

BACKGROUND OF THE INVENTION

Petroleum has become an essential part of our daily lives as it isimportant as a source of both energy and chemicals. There are, however,many problems associated with the recovery and processing of petroleum,such as the huge environmental impact associated therewith. In order toreduce the impact on environment, stringent policies and restrictionshave been implemented by many countries on petroleum products. Forexample, in many countries, including the United States, strictregulations have been implemented relating to the amounts and types ofsulfur compounds that can be included in motor gasoline and diesels.

These ever increasing demands for and stricter regulations on petroleumproducts poise inevitable challenge for the petroleum industry.Furthermore, the increasing supply of inferior petroleum sources, suchas heavy and sour crude oils, requires major breakthroughs in refiningtechnology to supply larger quantities of higher quality petroleumproducts to market. The recovery of petroleum from lower quality sourcesmeans that the petroleum that is recovered will likely include increasedamounts of impurities, such as sulfur and metals, and greaterpercentages of heavy oil fractions. This in turn requires increasedprocessing procedures designed to remove impurities and to convert theheavy fractions to more desirable and usable lighter fractions.Generally, the petroleum refining industry has relied upon conventionalmethods to clean and upgrade these lower quality petroleum feedstocks.

In general, conventional methods for cleaning and upgrading petroleumfeedstock can be classified into two groups: hydrogenative and thermalmethods. Hydrogenative methods, which can include hydrotreating andhydrocracking, typically employ hydrogen gas and a catalyst to removeimpurities and convert the heavier fractions into light and middle-rangepetroleum products. Thermal methods, which can include coking andvisbreaking typically do not utilize either hydrogen gas or a catalyst,instead relying upon relatively high temperatures for the conversion ofheavier fractions. These conventional technologies have been proven andoperated for long time.

Conventional methods, however, suffer from many limitations anddrawbacks. For example, hydrogenative methods typically require largeamount of hydrogen gas to achieve the desired level of upgrading anddesulfurization conversion. Additionally, hydrogenative methods alsorequire large amounts of catalyst, due to the frequent deactivation ofcatalyst. Thermal methods suffer from the production of large amount ofcoke as a byproduct and generally demonstrate limited success in theremoval of impurities, such as sulfur and nitrogen, and can result inthe production of large amounts of olefin and diolefin products, whichmust then be stabilized.

Thus, there exists a need to develop new methods for the upgrading ofcertain petroleum products that address and reduce the limitations anddrawbacks noted above.

SUMMARY

Generally, methods are provided for the supercritical water mediatedupgrading of petroleum feedstocks, particularly petroleum feedstocksthat include sulfur. The methods described herein utilize a start-upagent, which is effective for preventing the formation of coke, cokeprecursors, and sludge, and which allows the process to proceed moreeffectively than when the start-up agent is not employed.

In one aspect, a method for upgrading a petroleum feedstock withsupercritical water is provided that prevents plugging in processequipment lines. The method includes the steps of priming an upgradingreactor to receive the petroleum feedstock. The priming of the apparatusincludes the steps of supplying a heated and pressured water stream to afirst mixing device, wherein the water stream is heated and pressurizedto a temperature and pressure greater than the critical point of water.The priming step then includes the step of supplying a heated andpressurized start-up agent stream to the first mixing device, whereinthe start-up agent stream is heated and pressurized to a temperature ofbetween about 10 and 250° C. and mixing the heated and pressurized waterstream and the heated and pressurized start-up agent stream in the firstmixing device to produce a water and start-up hydrocarbon containingprimer stream. The water and start-up agent containing primer stream aresupplied to the upgrading reactor, said reactor being maintained at atemperature that is between about 380 and 550° C. to produce a treatedprimer stream, wherein the primer stream has a residence time in theupgrading reactor of between about 10 seconds and 60 minutes. Thetreated primer stream is cooled to a temperature of less than about 150°C. and depressurized. The cooled treated primer stream is then separatedinto treated primer gas and treated primer liquid phase streams, and thetreated primer liquid phase is separated into a recycle start-up agentstream and a recycle water stream. The priming step is continued untilthe temperature of the streams within the heater, supercriticalupgrading reactor and cooling devices are maintained to within 5% oftheir set point for a period of at least 10 minutes. Then, the flow ofthe start-up agent containing primer stream to the upgrading reactor isstopped and then a heated and pressurized petroleum feedstock issupplied to the first mixing device, wherein the heated and pressurizedpetroleum feedstock is maintained at a temperature of between about 10and 250° C. The heated and pressurized water stream and the heated andpressurized petroleum feedstock are mixed in the first mixing device toproduce a mixed water and start-up petroleum feedstock stream and thenthe mixed water and start-up petroleum feedstock stream are supplied tothe upgrading reactor, said reactor being maintained at a temperaturethat is between about 380 and 550° C. to produce an upgraded petroleumcontaining stream, wherein the mixed water and start-up petroleumfeedstock stream has a residence time in the upgrading reactor ofbetween about 10 seconds and 60 minutes. The upgraded petroleumcontaining stream is cooled to a temperature of less than about 150° C.and then depressurized. The cooled upgraded petroleum containing streamis separated into a gaseous phase upgraded and desulfurized petroleumcontaining stream and liquid phase upgraded and desulfurized petroleumcontaining stream, and the liquid phase upgraded and desulfurizedpetroleum containing stream is separated into an upgraded anddesulfurized petroleum product stream and a recycle water stream.

In certain embodiments, the water and start-up agent are each separatelyheated to a pressure greater than the critical pressure of water,alternatively between about 23 MPa and 30 MPa, alternatively betweenabout 24 MPa and 26 MPa. In certain embodiments the start-up agent isheated to a temperature of between about 10 and 250° C., alternativelybetween about 50 and 200° C., alternatively between about 100 and 175°C. In certain embodiments, the water can be heated to a temperature ofbetween about 250 and 650° C., alternatively between about 300 and 550°C., alternatively between about 400 and 550° C.

In certain embodiments, the supercritical water reactor is maintained ata temperature of between about 380 and 550° C., alternatively betweenabout 390 and 500° C., alternatively between about 400 and 450° C.Residence time of the reactants in the supercritical reactor is between1 second and 2 hours, alternatively between about 10 seconds and 1 hour,alternatively between about 30 seconds and 30 minutes, alternativelybetween about 1 minute and 20 minutes, alternatively between about 5minutes and 30 minutes, alternatively between about 30 seconds and 15minutes, alternatively between about 30 seconds and 10 minutes.

In certain embodiments, the product stream from the supercriticalreactor is cooled to a temperature of less than about 150° C.,alternatively to a temperature between about 5 and 150° C.,alternatively between about 10 and 100° C., alternatively between about25 and 75° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an embodiment of a prior art supercritical upgrading process.

FIG. 2 is an embodiment of a supercritical upgrading process accordingto one embodiment described herein.

FIG. 3 is a graph showing pressure in the line immediately upstream ofthe supercritical reactor in the embodiment shown in FIG. 3.

FIG. 4 is a graph showing pressure in the line immediately upstream ofthe supercritical reactor of an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Although the following detailed description contains many specificdetails for purposes of illustration, it is understood that one ofordinary skill in the art will appreciate that many examples, variationsand alterations to the following details are within the scope and spiritof the invention. Accordingly, the exemplary embodiments of theinvention described herein and provided in the appended figures are setforth without any loss of generality, and without imposing limitations,on the claimed invention.

Petroleum upgrading utilizing supercritical water is one of the mostpromising non-conventional approaches for the treatment anddesulfurization of whole crude oil and various process streams fromrefineries. The plugging of the process line through the formation ofcoke, coke precursor, or sludge, however, is one of the most serioustechnical challenges for the operation and scaling-up of the process.Localized heating or the creation of “hot spots” facilitatesinter-radical reactions, leading to the formation of coke precursors,coke and sludge. The use of supercritical water can suppress theinter-radical reactions that lead to the formation of these undesirablespecies. The methods described herein provide for a novel method forstarting-up of the process that is effective to the prevention of theformation of materials that may plug up the system.

As used herein, “petroleum feedstock” refers to crude oil, crude oilrefinery distillates, crude oil refinery residue, cracked products froma crude oil refinery, liquefied coal, bitumen, hydrocarbons thatoriginates from biomass, and the like.

As used herein, “upgrading” and “desulfurization” refers that product ofa process has higher API gravity, higher middle distillate yield, lowersulfur content, lower nitrogen content, lower metal content than thoseof petroleum feedstock that is supplied to the process.

As used herein, “supercritical water” is defined as water that ispresent at a temperature that is greater than about 374° C. and pressurethat is greater than about 21.1 MPa.

The present methods provide for the operation of a process for theupgrading and desulfurization of petroleum feedstock to produce apetroleum product having increased API gravity, increased middledistillate yield, decreased sulfur content, decreased nitrogen content,and decreased metal content. The process is conducted in the absence ofany externally supplied hydrogen, does not generate coke in the reactor,and does not result in the plugging of process lines.

More specifically, petroleum feedstock is supplied to a large upgradingreactor where it is contacted with supercritical water and at least aportion of the hydrocarbon molecules present are cracked and at least aportion of the impurities present in the feedstock, such as sulfur,nitrogen and metal-containing species, are removed. Advantageously, incertain embodiments, the treatment with supercritical water can beconducted in the absence of externally supplied hydrogen, in the absenceof a catalyst, and/or without generating coke in the process line andwithout plugging of process lines.

More specifically, the method of starting-up of the supercritical waterprocess described herein is designed to upgrade and desulfurize thepetroleum feedstock and prevent generation of coke in the process lineand plugging of process line, which can reduce the quality of petroleumproduct from the process and cause unexpected shut-downs that arenecessary for the.

This methods described herein utilize supercritical water, which canfunction as the reaction medium, catalyst, and source of hydrogen toupgrade petroleum. At supercritical conditions, the phase boundarybetween liquid and gas phases of water disappears. The resultingsupercritical water has various unique properties, and is quitedifferent from subcritical water. Supercritical water has very highsolubility with respect to organic compounds and is infinitelymiscibility with gases. Also, near-critical water (i.e., water that isat a temperature and pressure are very near to, but not exceed, thecritical point of water) has very high dissociation constant. This meanswater at near-critical conditions is very acidic. This acidity can beutilized as a catalyst for the upgrading and desulfurization ofpetroleum feedstocks. Furthermore, radical species in the presence ofsupercritical water may be stabilized through cage effect (generallyunderstood as what occurs when water molecule(s) surrounds radicals toprevent them interact). By stabilizing the radical species that arepresent, inter-radical condensation reactions are prevented, therebyreducing the amount of coke that is produced as a result ofinter-radical condensation, such as is found with polyethylene.Supercritical water is also capable of generating hydrogen through steamreforming reaction and water-gas shift reactions, which can then be usedfor upgrading petroleum.

In spite of many advantages that are associated with the use ofsupercritical water process for the upgrading and desulfurization ofpetroleum feedstock, there are still challenges that remain to besolved. One challenge is reducing or eliminating the frequent pluggingof process line by sludge or coke that is generated in the supercriticalwater reactor. The sludge or coke generation can be the result oflimited hydrogen being present in the reactor as the reaction proceeds.Because many of the embodiments described herein have limited hydrogenavailability, without the novel aspects of the present invention, therewould be a greater chance to generate coke precursor, coke, and sludge.Coke precursor, coke, and sludge are all representative of certainhydrocarbon compounds having hydrogen to carbon ratio of less than 1:1,and generally have no or very little solubility in supercritical water.

It is well known that plugging of the process lines, particularly thelines leading to and including the heat exchanger(s) and pressurelet-down device(s), can result in the unexpected increase of pressuredrop through the process line, and eventually result in the requiredshut-down of entire process to remove the materials that are pluggingthe equipment. Additionally, because the coke precursor, coke, andsludge have very low economic value, any production thereof results indecreased process economy because of loss/conversion of valuablepetroleum feedstock to low economic valued product.

Coke precursor, coke, and sludge can be generated throughinter-molecular or inter-radical condensation of certain aromaticmolecules to form polyaromatic compounds. The use of supercritical watercan, in certain embodiments, reduce or prevent the formation of thesecompounds. Without wishing to be bound by any specific theory, it isbelieved that supercritical water may have a stabilizing effect (alsoknown as “cage effect”), which can suppress inter-radical reactions,which generally occur at certain elevated temperatures, for example attemperatures greater than about 350° C., more specifically at atemperature greater than about 374° C. In certain embodiments, however,a portion of petroleum feedstock that may not be readily dissolved insupercritical water can undergo inter-radical reaction, which can leadto the generation of coke precursor, coke, and sludge through certaincondensation and/or polymerization reactions. While supercritical watercan dissolve most molecules found in crude oil, some molecules,particularly the heavy molecules, require additional time to dissolve.This can also occur when a portion of the petroleum feedstock that hasbeen heated to elevated temperature, temperatures greater than about350° C., outside of the presence of supercritical water or beforecontacting the supercritical water, experiences inter-radical reactionwhich eventually generates coke precursor, coke, and sludge.

In certain embodiments, during the initial stage of feeding thepetroleum feedstock into the reactor, coking can occur due to unstablephase balance between supercritical water and petroleum feedstock, whichis believed to be the result of a sudden increase of the concentrationof petroleum feedstock in the reactor. In certain embodiments, theformation of coke precursor, coke, and sludge can be eliminated byensuring a high dispersion of the petroleum feedstock in supercriticalwater. In certain embodiments, this may be one of the most importantsteps in this process. Mixing can be achieved by many different means,such as with a static mixer, an inline mixer, an impeller, or the like.In certain embodiments, the mixing can occur in a mixing zone that islocated upstream of the reactor, or alternatively it can take placewithin the reactor.

It is believed that in certain embodiments, the effectiveness of mixingof the supercritical water and the petroleum feedstock during theinitial feeding stage may be limited due to an unstable phase boundaryof the mixture of supercritical water and petroleum feedstock. This maybe due, in part, to a sudden increase of the concentration of thepetroleum feedstock in the reactor.

Referring now to FIG. 1, a comparative example is shown. The figureillustrates the an exemplary method for the upgrading anddesulfurization of a petroleum feedstock with supercritical water.Exemplary petroleum and hydrocarbon feedstocks can include, but are notlimited to, whole range crude oil, topped crude oil, product stream frompetroleum refinery processes, product streams from steam crackers,liquefied coal, liquid products recovered from oil sand, bitumen,asphaltene, and various hydrocarbons that originate from biomass. Incertain embodiments, the petroleum or hydrocarbon feedstock can have anAPI gravity in the range of about 1 to 40, a hydrogen/carbon molar ratioin the range of about 0.5 to 2.1, and a sulfur content in the range ofbetween about 0.1 to 7.5% by weight. In certain embodiments, thepetroleum or hydrocarbon feedstock can be an Arabian heavy crude oilhaving an API Gravity of about 28, and a sulfur content of about 3.1 wt% sulfur; a vacuum residue from Arabian heavy crude oil having an APIGravity of about 3, a sulfur content of about 6.0% by weight, and ahydrogen to carbon ratio of about 1.4:1; an atmospheric residue fromArabian heavy crude oil having an API gravity of about 4.5, a sulfurcontent of about 4.5% by weight, and a hydrogen to carbon ratio of about1.55:1; or an Athabasca bitumen having an API gravity of about 6, asulfur content of about 5.5% by weight, and hydrogen to carbon ratio ofabout 1.5:1.

Apparatus 100 is an apparatus for the upgrading and desulfurization of asulfur containing petroleum feedstock. Petroleum feedstock supplied vialine 102 and water supplied via line 108 can be supplied to first mixingdevice 112 to produce combined petroleum and water stream 114. Firstmixing device 112 can be selected from a static mixer, an inline mixer,an impeller, or like device. Water is supplied to apparatus 100 via line104, and is split into two water streams by splitter 106, which producesfirst water stream 108, which supplies water to mixer 112, and secondwater stream 110, which supplies a supercritical water stream to reactor132. Combined petroleum and water stream 114 is supplied to pump 116 toproduce pressurized combined petroleum and water stream 118.

Pressurized combined petroleum and water stream 118 can then be fed tofirst heating means 118, which is shown to be a heat exchanger, althoughit is understood that other known heating devices can similarly be usedto heat the pressurized combined petroleum and water stream to provide aheated and pressurized combined petroleum and water stream. In certainembodiments, heated and pressurized combined petroleum and water stream122 can be heated to a temperature of between about 30° C. and 300° C.,alternatively to a temperature of between about 50° C. and 150° C.

Water supplied via line 110 can be pressurized by pump 124 to producepressurized water stream 126. Pressurized water stream 126 can then besupplied to second heating means 128, which, while shown as a heatexchanger, can be any known heating means. Heating means 128 producesheated and pressurized water stream 130. Heated and pressurized waterstream 130 can be heated to a temperature of between about 300° C. and800° C., alternatively to a temperature of between about 400° C. and650° C.

In certain embodiments, the temperature of heated and pressurizedcombined petroleum and water stream is maintained at a temperature ofless than about 150° C. in an effort to prevent coke precursor, coke andsludge generation.

Heated and pressurized combined and water streams 122 and 130 are fed tosecond mixing device 132 to produce mixed stream 134. Second mixingdevice 132 can be a static mixer, an inline mixer, an impeller-embeddedmixer, or other mixing device known in the art. After the heated andpressurized combined and water streams 122, 130 have been mixed toproduce mixed stream 134, the mixed stream can be supplied to reactor136.

Reactor 136 can be a tubular type reactor, a vessel type reactorequipped with a stirrer or other means for providing mixing oragitation, or like apparatus, and can be vertical, horizontal, or bothvertical and horizontal. In certain embodiments, the reactor does notinclude baffles. Reactor 136 can be maintained at a temperature that isgreater than the critical temperature of water (i.e., at a temperaturethat is greater than about 374° C.), alternatively between about 380° C.and 600° C., alternatively between about 390° C. and 450° C. Within thereactor, the petroleum feedstock is treated with supercritical water toupgrade and desulfurized the feedstock and product an upgradedhydrocarbon containing stream 138

Upgraded hydrocarbon containing stream 138 can be supplied from reactor136 to cooling means 140, to reduce the temperature of the upgradedhydrocarbon containing stream. Cooling means 140 is shown as a heatexchanger, although it is understood that any means for reducing thetemperature of stream 138, such as a chiller, can also be employed. Incertain embodiments, cooling means 140 can be a heat exchanger having adouble pipe, shell-and-tube type, or other configuration known in theart. The temperature of upgraded hydrocarbon containing stream 142 canbe between about 10° C. and 200° C., alternatively between about 30° C.and 150° C. The pressure of stream 142 can be reduced by let-down device144, which can be pressure regulator or other similar device known inthe art. Upstream of let-down device 144, the pressure in upgradedhydrocarbon containing stream is maintained at between about 3200 psigand 6000 psig, alternatively between about 3300 psig and 4500 psig.Let-down device 144 can reduce the pressure of stream 142 from betweenabout −30 psig and 30 psig. Suitable depressurizing devices can includea pressure regulating valve, capillary tube, or other device known inthe art.

In certain embodiments, the product stream from reactor 136 can be heatexchanged with the start-up stream or water, wherein the start-up streamor water is heated and the product stream is cooled by the process.

The general start-up procedure for the apparatus shown in FIG. 1 is asfollows. Water supplied via line 104 to splitter 106 fed to first mixingdevice 112, first pump 116 and first heater 120. A valve (not shown) inpetroleum feed line 102 is closed such that only water is being suppliedto first pump 116 and first heater 120. At the same time, water issupplied via line 110 to second pump 124 and second heater 128. Thefirst and second heaters 120 and 128 and reactor 136 are heat topre-determined levels. Cooling means 140 is then started to achieve andmaintain the temperature at a certain pre-determined level. Aftercertain amount of time after the starting of first and second pumps 116and 124, the pressure of the system is increased to a pre-determinedlevel by controlling let-down device 144.

After the temperature of first and second heaters 120 and 128 andreactor 136 reach a pre-determined temperature, a valve (not shown)positioned within line 108 is closed, and the valve positioned withinline 102 is opened, thereby supplying the petroleum feed to first mixingdevice 112, first pump 116, first heater 120, and second mixing device132. The flow rate of the petroleum feedstock to the apparatus can becontrolled by controlling the opening and/or closing of the valvespositioned within lines 102 and 108.

In general, it is inevitable that there will be a transition periodwhere an unstable phase boundary between petroleum feedstock and waterexists. In particular, the heavy fraction of petroleum feedstock, forexample, an asphaltene fraction, can be segregated from the remainder ofthe petroleum feedstock present in the reactor, which can eventuallylead to coking. In certain embodiments, during the transition period, apart of petroleum feedstock may experience localized heating (i.e.,heating in the absence of supercritical water), which can lead to thegeneration of coke precursor, coke, and sludge. Coke, coke precursor,and sludge are all undesired as they can lead to a blockage of thelines, and shut-down of the process. In general, a small amount of coke,coke precursor, or sludge can lead to a blockage between the reactor andcooler, which will require that the process be shut-down due to theresulting pressure drop. Lines must be cleaned and/or replaced, leadingto significant down time and economic loss.

FIG. 2 shows an example of supercritical water process to upgrade anddesulfurized petroleum feedstock according to one embodiment of thepresent invention.

Apparatus 200 is provided for the upgrading and desulfurization of apetroleum feedstock. A start-up agent and petroleum feedstock areprovided to first mixing device 214 via lines 202 and 204, respectively.Water is supplied to splitter 208 via line 206, which splits the waterinto lines 210 and 212, which supply a first water stream and a secondwater stream, respectively. The first water stream supplied via line 210to first mixing device 214. First mixing device 214 can be any suitablemeans for mixing fluid streams of varying viscosity, including but notlimited to a static mixer, an inline mixer, an impeller-embedded mixeror other mixing device known in the art. Lines 202, 204, and 210 caneach include various valves and pumps, as may be necessary to controlthe flow of fluids therethrough.

First mixing device 214 can combine the various feeds to supply line216. Line 216 can include first pump 218 and first preheater 222, and issupplied to second mixing device 234. Line 212 can include second pump226 and second preheater 230, and is supplied to second mixing device234. Second mixing device 234 can be any suitable means for mixing fluidstreams of varying viscosity, including but not limited to a staticmixer, an inline mixer, an impeller-embedded mixer or other mixingdevice known in the art. Preheater 222 can be capable of heating fluidsprovided thereto up to a temperature of between about 30 and 300° C.,alternatively between about 50 and 150° C. Preheater 230 is capable ofheating a pressurized water stream provided thereto up to a temperatureof between about 300 and 800° C., alternatively between about 400 and650° C. In certain embodiments, petroleum feedstock supplied to firstpreheater 222 is not heated to a temperature that is greater than about150° C., to prevent or reduce the generation of coke precursor, coke,and sludge.

Second mixing device 234 can produce a mixed stream that exits the mixervia line 236, and is supplied to reactor 238. Reactor 238 can have avertical, horizontal, or combined orientation. Reactor 238 can be atubular type reactor, a vessel type reactor, or like apparatus, and canbe equipped with means for providing mixing, include a stirrer or otherknown means. The temperature within reactor 238 is maintained at atemperature that is greater than the critical temperature of water(i.e., at a temperature that is greater than about 374° C.). In certainembodiments, the reactor temperature is maintained in the range of about380 to 600° C., alternatively at a temperature of between about 390 to475° C., alternatively at a temperature of between about 400 to 460° C.In certain embodiments, the temperature is between about 400 to 450° C.Residence time of the reactants in reactor 238 can be between 1 secondand 120 minutes, alternatively between 5 seconds and 60 minutes,alternatively between about 10 seconds and 30 minutes, alternativelybetween about 30 seconds and 30 minutes, alternatively between 30seconds and 20 minutes, alternatively between about 30 seconds and 10minutes. In certain embodiments, the residence time is between about 1and 30 minutes, alternatively between about 2 and 20 minutes. In certainembodiments, the residence time will not exceed 15 minutes, such thatthe residence time is between about 2 and 15 minutes. The product streamexits reactor 238 via line 240, and can be supplied to heat exchanger orcooler 242, designed to reduce the temperature of the fluids carried vialine 240, and pressure let down device 246, designed to reduce thepressure of the fluids exiting the reactor. Cooler 242 can be a chilleror heat exchange of double pipe or shell-and-tube type, or other form asknown in the art. Cooler 242 reduces the temperature of the productstream carried in line 240 such that the product stream in line 244 isat a temperature of between about 10 and 200° C., alternatively betweenabout 30 and 150° C., alternatively between about 10 and 100° C.,alternatively between about 25 and 70° C. Pressure let down device 246reduces the pressure in stream 244 such that the pressure of the fluidsin stream 248 is reduced from between about 3200 psig and 6000 psig,alternatively between about 3300 psig and 4500 psig, to within the rangeof between about −30 psig and 30 psig, alternatively between about −10pisg and 10 psig. Pressure of streams before Let-Down Device ismaintained in the range of about 3,200 psig to 6,000 psig, morepreferably, about 3,300 psig to 4,500 psig. The pressure let-down devicecan be a pressure regulating valve, capillary tube, or other device asis known in the art.

The start-up procedure for apparatus 200, as provided in FIG. 2, is asfollows. The procedure begins as a valve in line 210 is closed and wateris supplied via line 206 to splitter 208, which supplied water via line212 to second pump 226. At the same time, a valve within line 204 isclosed to prevent supply of the petroleum feedstock to first mixingdevice 214. A start-up agent, such as toluene, is fed line 202 to firstmixing device 214, which supplies the start-up agent via line 216 tofirst pump 218. First and second preheaters 222 and 230 are heated topre-determined levels, as provided previously. Cooler 242 is operated ata pre-determined level. The start-up agent can be selected based uponhigh miscibility with supercritical water, and be readily available in aconventional refining process.

After certain time from starting pumps, or alternatively after thepreheaters have been heated to a pre-determined levels, pumps 218 and226 and let down device 246 are operated such that pre-determinedpressures are achieved within the system. After a predetermined amountof time has allowed apparatus 200 to reach pre-determined temperaturesand pressures, a valve within line 202 is closed, thereby stopping theflow of the start-up agent to the first mixing device 214, and a valvewithin line 204 is opened, thereby allowing the petroleum feedstock tobe supplied to the first mixing device. According to this procedure, thepetroleum feedstock can be supplied to the system (and ultimately toreactor 238) in a step-wise fashion. Alternatively, the flow of thepetroleum feedstock to mixing device 214 and line 216 exiting therefromcan be gradually increased while maintaining a constant pressure offluids within line 216 by controlling the opening of the valvepositioned within line 204, and the closing of the valve positionedwithin line 202.

During the transition period as the flow of the start-up agent to thesystem is decreased and stopped, and the flow of the petroleum feedstockis started and gradually increased, the petroleum feedstock is wellmixed with supercritical water because the step of supplying thestart-up agent to the system provides a very stable fluid and pressurein lines 216, 220 and 224 located between first mixing device 214 andsecond mixing device 234. Use of the start-up agent allows forcontinuous operation of the process, as the start-up agent preventsand/or reduces plugging of the process equipment that typically resultsfrom the formation of sludge, coke, and coke precursors. In general,once a process line becomes plugged, pressure within the line drops,thereby accelerating the formation of sludge, coke or coke precursors,and accelerating the plugging of the equipment.

In certain embodiments, the start-up agent can create favorable fluidconditions within the system for the step of supplying and processingcertain petroleum feedstocks. By creating the favorable fluid conditionswith the use of the start-up agent prior to the step of supplyingpetroleum feedstock, mixing of the petroleum feedstock and supercriticalwater in second mixing device 234 is improved. The start-up agentincreases the ability for the supercritical water to solubilize thepetroleum feedstock, particularly heavy hydrocarbons. This leads to adramatic and unexpected reduction in the production of coke, cokeprecursors, and sludge within reactor 238, which occur when the start-upagent is not employed. The production of coke, coke precursors, andsludge is particularly common when the petroleum feedstock includesheavy hydrocarbons, such as asphaltenes.

Exemplary start-up agents can be selected from the pure hydrocarbons ora mixture of hydrocarbons, generally having a boiling point that rangesfrom about 30° C. and about 250° C., alternatively between about 30° C.and about 90° C., alternatively between about 90° C. and about 150° C.,alternatively between about 150° C. and about 250° C. The start-up agentcan have an aromatic compound content of between about 30 and 100% byvolume, alternatively between about 30 and 50% by volume, alternativelybetween about 50 and 75% by volume, alternatively between about 75 and95% by volume, alternatively at least about 95% by volume. Generally,the start-up agent can have a solid matter content of less than 10% byweight, alternatively less than about 5% by weight, alternatively lessthan about 2% by weight, alternatively less than about 1% by weight.Alternatively, the start-up agent can have a solid content of less thanabout 25 ppm by weight, alternatively less than about 15 ppm by weight,alternatively less than about 10 ppm by weight, alternatively less thanabout 5 ppm by weight.

In certain embodiments, the start-up agent can be selected from aromatichydrocarbons, such as benzene, toluene, o-xylene, m-xylene, p-xylene,ethylbenzene, and combinations thereof. In certain embodiments, thestart-up agent can be a product from a refining process, such asreformate from catalytic reformer, light cracked naphtha from an FCC,visbreaker naphtha, coker naphtha, and the like. In certain embodiments,the start-up agent can a product selected from a petrochemical process,such as the product of the pyrolysis of gasoline from steam cracker.

In general, the selected start-up agent (for example, toluene) can bereadily mixed with supercritical water (for example, the water suppliedto mixer 234 via line 232, as shown in FIG. 2), in part because it haslow CST (i.e., critical solution temperature). At temperatures greaterthan the CST of the start-up agent, the start-up agent is typicallyfully mixed with solvent (in this case, water). The CST of toluene hasbeen reported to be about 308° C. at about 220 atm. Thus, atsupercritical conditions, the mixture of water and toluene is well mixedand has very high solvent power toward hydrocarbons. The high solventpower of the mixture of water and the start-up agent is believed tofacilitate immediate mixing of the petroleum feedstock intosupercritical water provided via line 232.

In certain embodiments, with the apparatus shown in FIG. 1, the rapidand sudden injection of a petroleum feedstock, regardless of the rate ofinjection of said petroleum feedstock, causes a localized agglomerationof a portion of the petroleum feedstock in mixer 234, reactor 238 andline 236 connecting the mixer and the reactor. Such localizedagglomeration spots are the result of poor mixing, and can lead to theconversion of hydrocarbon feedstock into coke precursor, coke, andsludge. Once the coke precursor, coke, and sludge has been formed, theprocess lines of the equipment are vulnerable to plugging, which canthen induce a pressure drop throughout the process lines of theapparatus, resulting in the unexpected but necessary shut-down of theprocess.

One major advantage of upgrading a hydrocarbon or petroleum feedstockusing the apparatus provided in FIG. 2 is that the apparatus provides amore intimate mixing of the petroleum feedstock and the supercriticalwater. The start-up agent and water provide a fully mixed fluid havinghigh solvent power toward the hydrocarbon or petroleum feedstock thatcan be formed in line 236, positioned between second mixing device 234and reactor 238, before petroleum feedstock is injected into the system.Thus, the front wave of the petroleum feedstock that is injected intothe system contacts a fully mixed fluid that includes supercriticalwater and the start-up agent, and can be readily mixed into the fluid,due in part to the high solvent power of the fluid. Even after the flowof the start-up agent is stopped and the flow of the petroleum orhydrocarbon feedstock to the apparatus is started, the fluids withinline 236 are fully mixed and do not include portions of petroleum orhydrocarbon that aggregate together, as is the case with the apparatusof FIG. 1. Even after the supply of the start-up agent to the apparatushas been stopped, use of the apparatus of FIG. 2 provides for theformation of a stable, homogeneous mixture (i.e., the apparatus providesa homogenous mixture of the petroleum feedstock and supercriticalwater), and also provides light hydrocarbons which can be generatedthrough the upgrading reaction by contacting the petroleum feedstockwith supercritical water in second mixing device 234. The lighthydrocarbons generated by the step of contacting the supercritical waterand petroleum feedstock can have properties that are similar to theproperties of the start-up agent, and facilitate the mixing of incomingpetroleum or hydrocarbon feedstock into supercritical water.

EXAMPLES

In the following examples, pilot-scale reactor systems having thecomponents shown in FIGS. 3 and 5 were utilized, respectively. Thepetroleum feedstock that was utilized was Arabian heavy crude oil havinga total sulfur content of about 3.1 wt %, a total metal content of about63 ppm (by weight), an API gravity (at about 60° F.) of 26, and residhaving boiling point of over 483° C.+=34 vol %).

Example 1

Referring now to FIG. 3, a deionized water tank (upstream from waterline 104, not shown) and a crude oil tank (upstream from crude oil line102, not shown) were filled with deionized water and Arabian heavy crudeoil, respectively. Valve 103 positioned in line 102 and valve 105 inline 104 were each opened. Two high pressure pumps were connected to thedeionized water tank T1, a were set at a volumetric flow rate of about1.5 L/hr STP, and water was fed into the process lines 108 and 110.Pre-heaters positioned in lines 102 and 108 were set to temperatures of538° C. and 150° C., respectively. Reactor 136 consisted of twovessel-type reactors connected in series. First vessel-type reactor hadan impeller-type agitator inside to facilitate mixing of feed stream,wherein the rotating speed of the impeller was approximately 600 rpm.Both the first and second vessel-type reactors were maintained at atemperature of about 380° C. and the temperature therein was monitoredwith multiple thermocouples positioned within each reactor. Temperaturesof reactor internal fluids were controlled with the thermocouples placedin the most downstream position of the reactor. The product stream fromreactor 136 was cooled with double pipe-type heat exchanger 140 toreduce the temperature of the stream to less than 100° C. The pressurewithin the line was released by back pressure regulator 144. Operatingpressure of the reactor was maintained at about 250 Bar.

After allowing the temperature within each piece of equipment tostabilize at predesignated levels, valve 103 was opened and valve 105was simultaneously closed to change feed to line 114 from deionizedwater from the water holding tank to the Arabian heavy crude oil fromthe crude oil tank. FIG. 3 shows a measure of the pressure measured by apressure sensor located just upstream from the inlet of reactor 136,which shows a relatively sudden and rapid increase in the pressurewithin the line due to plugging as a result of the formation of coke,coke precursor, and sludge. After the pressure measured by the pressuresensor reached a pre-designated safety limit (set here at 360 Bar), thewhole reactor system shut-down by a safety interlock. The totaloperation time, once the flow of the petroleum feedstock was initiated,was less than 25 minutes.

Example 2

Referring now to FIG. 2, start-up agent feed tank (upstream fromstart-up line 202, not shown) was integrated to a pump through valve203. A storage tanks filled with deionized water was fluidly connectedto line 206 and another storage tanks filled with Arabian heavy crudeoil was fluidly connected to line 204. The properties of the start-upagent are provided in Table 1. Pumps were connected to water storagetank and start-up agent storage tank by manipulating one or more valves.After setting the pumps at a volumetric flow rate of 1.0 l/hr at STP,water and the start-up agent were fed to the process line 216.Pre-heaters 222 and 230 were set at temperatures of about 150° C. and550° C., respectively. Reactor 238 consisted of two vessel type reactorsconnected in series, wherein the first reactor had impeller-typeagitator operated at 600 rpm to facilitate mixing of feed stream. Thetemperatures of two reactors connected in series were set to 390° C. andmonitored using multiple thermocouples per reactor. The temperature ofreactor fluids were controlled using a thermocouple positioned at themost downstream position of the reactor. The product stream from thesecond reactor was cooled by double-pipe type heat exchanger 242 to atemperature of less than 100° C. Pressure was released by back pressureregulator 246. During operation, a pressure of about 250 Bar wasmaintained.

After the temperature within each piece of equipment was stabilized atpredesignated levels, the feed to the pump was changed from the start upagent via line 202 to Arabian heavy crude oil supplied via line 204 asvalve 203 was closed and valve 205 was opened. As shown in the FIG. 4,pressure measured at a position located just upstream of reactor 238remained constant at the pre-designated value of 250 Bar. In thisexample, the apparatus operated for a total operation time of 400minutes without experiencing any plugging of the process lines. Thetotal sulfur content of product was 31% lower than that of Arabian HeavyCrude Oil feedstock, and total metal content (i.e., the sum of nickeland vanadium contents) decreased to 85% of original content. API gravityof the product increased by 5 as a result of the supercritical watermediated upgrading.

TABLE 1 Start-up agent Properties. Start-up agent Composition (vol. %)Paraffins Isoparaffins Olefins Naphthenes Aromatics Unknown 12.7 31.4 11.2 53.3 0.4 Distillation (ASTM D-86) (volume %, ° C.) IBP 10% 20% 30%40% 50% 60% 70% 80% 90% 95% EP 38 74 88 97 105 113 122 131 140 151 161183

It is understood that the various figures provided herein to assist inthe understanding of the various embodiments of the invention may notshow all of the valves and pumps necessary for the operation thereof.One of skill in the art would understand that various pumps and valvescan be placed within one or more process line to facilitate theoperation thereof.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions, and alterations canbe made hereupon without departing from the principle and scope of theinvention. Accordingly, the scope of the present invention should bedetermined by the following claims and their appropriate legalequivalents.

The singular forms “an” and “the” include plural referents, unless thecontext clearly dictates otherwise.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value and/or to the other particular value, along withall combinations within said range.

Throughout this application, where patents or publications arereferenced, the disclosures of these references in their entireties areintended to be incorporated by reference into this application, in orderto more fully describe the state of the art to which the inventionpertains, except when these references contradict the statements madeherein.

As used herein and in the appended claims, the words “comprise,” “has,”and “include” and all grammatical variations thereof are each intendedto have an open, non-limiting meaning that does not exclude additionalelements or steps.

As used herein, terms such as “first” and “second” are arbitrarilyassigned and are merely intended to differentiate between two or morecomponents of an apparatus. It is to be understood that the words“first” and “second” serve no other purpose and are not part of the nameor description of the component, nor do they necessarily define arelative location or position of the component. Furthermore, it is to beunderstood that that the mere use of the term “first” and “second” doesnot require that there be any “third” component, although thatpossibility is contemplated under the scope of the present invention.

That which is claimed is:
 1. A method for upgrading a petroleumfeedstock with supercritical water while preventing plugging inequipment process lines, the method comprising the steps of: priming anupgrading reactor to receive the petroleum feedstock, the priming of theapparatus comprising the steps of: supplying a heated and pressuredwater stream to a first mixing device, wherein the water stream isheated and pressurized to a temperature and pressure greater than thecritical point of water; supplying a heated and pressurized start-uphydrocarbon stream to the first mixing device, wherein the start-uphydrocarbon stream is heated and pressurized to a temperature of betweenabout 10 and 250° C.; mixing the heated and pressurized water stream andthe heated and pressurized start-up hydrocarbon stream in the firstmixing device to produce a water and start-up hydrocarbon containingprimer stream; supplying the water and start-up hydrocarbon containingprimer stream to the upgrading reactor, said reactor being maintained ata temperature that is between about 380 and 550° C. to produce a treatedprimer stream, wherein the primer stream has a residence time in theupgrading reactor of between about 10 seconds and 60 minutes; coolingthe treated primer stream to a temperature of less than about 150° C.,depressurizing the cooled treated primer stream; separating the cooledtreated primer stream into treated primer gas and treated primer liquidphase streams; separating the treated primer liquid phase into a recyclestart-up hydrocarbon stream and a recycle water stream; continuing thepriming step until the temperature of the streams within the heater,supercritical upgrading reactor and cooling devices are maintained towithin 5% of their set point for a period of at least 10 minutes;stopping the flow of the start-up hydrocarbon containing primer streamto the upgrading reactor and then supplying a heated and pressurizedpetroleum feedstock to the first mixing device, wherein the heated andpressurized petroleum feedstock is maintained at a temperature ofbetween about 10 and 250° C.; mixing the heated and pressurized waterstream and the heated and pressurized petroleum feedstock in the firstmixing device to produce a mixed water and start-up petroleum feedstockstream; supplying the mixed water and start-up petroleum feedstockstream to the upgrading reactor, said reactor being maintained at atemperature that is between about 380 and 550° C. to produce an upgradedpetroleum containing stream, wherein the mixed water and start-uppetroleum feedstock stream has a residence time in the upgrading reactorof between about 10 seconds and 60 minutes; cooling the upgradedpetroleum containing stream to a temperature of less than about 150° C.,depressurizing the cooled upgraded petroleum containing stream;separating the cooled upgraded petroleum containing stream into agaseous phase upgraded and desulfurized petroleum containing stream andliquid phase upgraded and desulfurized petroleum containing stream;separating the liquid phase upgraded and desulfurized petroleumcontaining stream into an upgraded and desulfurized petroleum productstream and a recycle water stream.
 2. The method of claim 1, wherein thestart-up hydrocarbon is selected from benzene, toluene, xylene, andethylbenzene.
 3. The method of claim 1, wherein the start-up hydrocarbonis selected from refromate from a catalytic reformer, light crackednaphtha from an FCC unit, visbreaker naphtha, coker naphtha, andpyrolysis gasoline from a steam cracker.
 4. The method of claim 1,wherein the start-up hydrocarbon has an aromatic content of at leastabout 30% by volume.
 5. The method of claim 1, wherein the start-uphydrocarbon has a solid content of less than about 10 ppm.
 6. The methodof claim 1, wherein the petroleum feedstock is selected from the groupconsisting of whole range crude oil, topped crude oil, the productstream from a petroleum refinery, the product stream from a steamcracker, liquefied coal, the liquid product recovered from oil sand,bitumen, asphaltene, and hydrocarbons that originate from biomass. 7.The method of claim 1, wherein the water, start-up hydrocarbon andpetroleum feedstock streams are each pressurized to a pressure that isgreater than the critical pressure of water.
 8. The method of claim 1,wherein the volumetric flow rate of the start-up agent and water isbetween 1:5 and 1:1.
 9. The method of claim 1, wherein the water isheated to a temperature of between about 300 and 550° C.
 10. The methodof claim 1, wherein the reactor is maintained at a temperature ofbetween about 400 and 450° C.
 11. The method of claim 1, the mixed waterand start-up petroleum feedstock stream has a residence time in theupgrading reactor of between about 20 and 30 minutes.
 12. The method ofclaim 1, wherein the step of cooling the upgraded petroleum containingstream exiting the upgrading reactor comprises supplying the stream to aheat exchanger wherein the stream is heat exchanged with a start-uphydrocarbon or water stream.
 13. The method of claim 1, wherein theupgraded petroleum containing stream is cooled to a temperature ofbetween about 25 and 75° C.
 14. The method of claim 1, wherein thepressure of upgraded petroleum containing stream exiting the upgradingreactor is reduced to between about 0.1 and 0.5 MPa.
 15. The method ofclaim 1, further comprising recycling the recycle start-up hydrocarbonstream to the first mixing device.
 16. The method of claim 1, furthercomprising recycling the recycle water stream to the first mixingdevice.